Update v8 to 7.4 for public and private class fields

[dlespiau]

v8 7.2 comes with public class fields, 7.4 implements private ones: https://v8.dev/blog/v8-release-74.

These fields would be handle to have private properties in object that can be used by methods without appearing in the rendered YAML/JSON.

Note it's possible to specify a toJSON method on values that will be used by JSON.stringify. Private fields would be really just a syntactic sugar to achieve the same thing.